Python · Lesson 3 of 9

Strings

f-strings, common string methods, indexing and slicing.

Strings hold text. The most useful tool is the f-string: put f before the quotes and write variables inside { }.

Handy methods

.upper(), .lower(), .title(), .strip() (remove spaces at both ends), .replace(a, b), .split(",") (text → list) and ", ".join(list) (list → text). Methods return a new string; the original is unchanged.

Indexing and slicing

Each character has a position starting at 0. s[0] is the first, s[-1] the last, and s[0:4] takes characters 0 to 3. len(s) gives the length.

Try it yourself

Code editor

Press Run to see the output.

Edit and press Run (or Ctrl/⌘ + Enter). Python runs in your browser — the first run downloads the Python engine and takes a few seconds.

Key points

f"...{value}..." formats text cleanly.
String methods return new strings.
Indexes start at 0; negative indexes count from the end.

Quick check

What is "Kerala"[-1]?

"K" "a" "l" An error

Practice task

Given email = " Anu.Kumar@Example.COM ", print it trimmed and in lower case, then print only the part before the @.

Interview corner

How do you reverse a string in Python?

Use a slice with step -1: text[::-1]. It returns a new reversed string.

Why are strings immutable and what does that mean in practice?

You cannot change a character in place (s[0] = 'x' fails). Every change produces a new string, which makes strings safe to share and usable as dictionary keys.